Ethylidene diacetate (EDDA) is a valuable chemical which can be used as an intermediate in preparing a wide variety of commercially valuable compositions such as vinyl acetate and acetic acid. Considerable interest has been focused on developing improved processes for preparing EDDA wherein problems associated with prior art methods can be overcome.
The condensation reaction of acetaldehyde and acetic anhydride to EDDA is a known chemical reaction catalyzed, for example, by Lewis and protonic acids. U.S. Pat. No. 2,859,241 discloses a process for preparing EDDA wherein acetaldehyde and an alkanoic anhydride such as acetic anhydride are reacted in the presence of an aromatic sulfonic acid such as benzenesulfonic acid to produce EDDA. A commercial process based on the foregoing disclosure is described in Hydrocarbon Process 44 (1965) 287.
U.S. Pat. No. 4,843,170 discloses a process for preparing EDDA wherein acetaldehyde and/or dimethylacetal and acetic anhydride are reacted to form EDDA as a reaction intermediate wherein EDDA is further cracked to form vinyl acetate. While no catalysts are required in the EDDA step, the reference states that acid catalysts such as a Bronsted acids, i.e. HI, HBr, HCl, HF, H.sub.2 SO.sub.4, HNO.sub.3, H.sub.3 PO.sub.4, H.sub.3 BO.sub.3, HClO.sub.3, HBrO.sub.3, HIO.sub.3, polyphosphoric acid, benzenesulfonic acid and alkylbenzenesulfonic acid or Lewis acids of halides having a central atom selected from Groups IIa, IIIa, IVa, Va, IIIb, IVb, Vb, VIb, VIIb and VIII of the Periodic Table can be used.
European Patent Specification No. 0 028 515 teaches a process for producing EDDA wherein one or a mixture of compounds selected from (1) dimethyl acetal, (2) acetaldehyde and methyl acetate, and (3) acetaldehyde and dimethyl ether are reacted in the presence of a catalyst. Suitable catalysts comprise compounds formed from at least one metal belonging to Group VIII of the Periodic Table and at least one compound selected from iodides, bromides and mixtures thereof.
Chem. Abstracts 1967-91, Vol. 114, #4, of a Russian article, Ukr. Khim.Zh., Vol. 56(1), pages 101-3 discloses that the reaction rate of acetaldehyde with acetic anhydride is inhibited in the presence of alkali-metal or alkali earth metal salts. The inhibiting activity decreases in the series of K.sup..about. Na.sup..about. L&gt; Ba&gt;Sr&gt;Ca&gt;Mg&gt;Al and such inhibiting effect was stated to be independent of the anion. Data presented in these Russian studies would lead to the conclusion that alkali metal iodides inhibit the reaction between acetaldehyde and acetic anhydride.
The prior art describes the carbonylation and hydrocarbonylation of methyl acetate to acetic anhydride and methyl acetate to form EDDA, respectively. In addition, mixtures of methyl acetate (MA) and dimethyl ether (DME) or dimethyl ether by itself are often mentioned as equivalent feedstocks. However, dimethyl ether and methyl acetate are not chemically equivalent feedstocks. Group VIII catalysts, organic iodides, synthesis gas composition, reaction temperatures and pressures, and dipolar solvents play a potential role differentiating the reactivity of DME and MA.
Considerable interest abounds in discovering a process for preparing EDDA in high yield under substantially anhydrous conditions. The instant patent application presents a process which overcomes many of the limitations associated with prior art processes. Specifically, the instant process provides high selectivity to EDDA and can be practiced utilizingg a broad range of feedstocks.